Uses
Early copy protection schemes deliberately introduced read errors on the disk, the software refusing to load unless the correct error message was returned. The general idea was that simple disk copy programs were incapable of copying the errors. When one of these errors was encountered, the disk drive (as do all disk drives) would attempt one or more re-read attempts after first resetting the head to track zero. Few of these schemes had much deterrent effect, as various software companies soon released "nibbler" utilities that enabled protected disks to be copied and, in some cases, the protection removed.
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